Ek Hasina Thi is about a travel agent called Sarika ( Urmila Matondkar) who is a single working woman living in Mumbai. By chance she bumps into Karan Rathore, a dapper and mysterious stockbroker who takes a fancy towards her. They draw closer and Sarika falls in love with Karan. That's when the fairytale ends and the nightmare begins.
Sarika is unintentionally drawn into a world of international crime, wrongfully accused of smuggling and imprisoned. In the prison, Karan's manipulative nature dawns upon Sarika. Her personality undergoes a radical change; from a mild-mannered simpleton she transforms into a wronged and vindictive woman who won't stop until she has avenged all those responsible for her predicament.... and Karan is the most wanted person on her list